Electric discharge lamp



J 1946- E. LEMQMERS 2,403,184

ELECTRIC DISCHARGE LAMP Filed Dec. 26, 1942 hwen'tor Eu ene Lemmers,

' His Air torneg.

Patented Jul 2, 1946 I we" ELECTRIC DISCHARGE LAMP Eugene Lemmers, Cleveland Heights, Ohio, assignor to General Electric Company, a corporatlon of New York ApplicationDecember 2c, 1942, sills: No. 470,119 3 Claims. (Cl. 176-122) My invention relates to gaseouselectric discharge devices and more particularly to discharge lamps of the cathode glow type. An object of my invention is to provide a lamp of this type which starts readily at low voltages and at the same time-has a good light output. A feature of the invention is an arrangement-of the cathode and anode such that they are closely spaced for easy starting, yet the discharge gap therebetween is substantially longer than the said spacing so that the lamp will have a good light output, this being accomplished without making either of the electrodes movable. Further features and objects of my invention will appear from the following description of a species thereof and from the drawing:

The single figure of the drawing is a perspective view of one species of lamp comprising my invention, together with a circuit therefor.

In one of its specific forms, the present inven= tion may be considered as a modification of the type of lamp shown in application Serial No. 387,002, G. E. Inman et al.,fi1ed April 5, 19%, now Patent No. 2,341,990, dated February 15, 1944. The lamp shown in that application operates satisiactorily and with good efliciency from a source of current supply having a potential of about 24.- volts. Lamps made in accordance with the present invention are capable of starting and operating on an approidmately 12 volt circuit.

I have found that in a lamp of the type disclosed in the above-mentioned application if the anode is moved closer to the cathode, in general the light output slowly diminishes until at a spacing of the anode about two millimeters from the point on the cathode at which the cathode spot occurs, about ten per cent of the light output is lost. Up to this point very little change occurs in the arc volts or ability to start. However, as the anode is moved closer to the cathode, the discharge voltage may drop about ten per cent and the ability to start improves considerably; However, about forty percent more of the light output is lost when the anode is moved closer than about 2 millimeters to the cathode spot.

I have found that by placing the anode within one millimeter of the coiled cathode, and three to five millimeters from that part of the cathode where the spot forms, I am able to retainall the starting advantages of the closer spaced anode without the lossfof light output. Such lamps start readily on 12 volt circuits and have are voltages of from 6.25 to 8.5 volts.

' Referring to the drawing, the particular form of lamp shown therein comprises a sealed'slass envelope Ill containing a suitable ionizable me? dium. The envelope may contain a fluorescent material as disclosed in the lumen et 'al. application referred to above, and, it may be made of 5 a vitreous material which is transparent to ultra-' violet rays where such radiation is to be utilized externally of the envelope. The ionizable medium may consist of a rare gas or a vaporizable material or mixtures thereof. I prefer to employ a mixture of argon and. a small amount of mer cury, the argon being at a pressure of, for example, .5 to 8 millimeters Hg, preferably a pressure of 3.5 to 4.5 millimeters.

The envelope contains a cathode ll and an lead-in conductors it and M, and the anode being mounted on a lead-in conductor 55. The conductors it, i l, and i5 extend through a conventional stem. it. 2i The cathode l l is preferably a, triple coil of the type disclosed and. claimed in Patent No. 2,306,925, J. 0. Aicher, dated vDecelnoimr 29, 1942, and is coated with an electron-emissive material, preferably an alkalineearth oxide," or mixtures thereof, such as barium and strontium oxides. For the specific lamp shown in the drawing, which may be rated at about 3 watts, the cathode ll may be made to the following specifications, The cathode wire may be tungsten having a diameter of .35 to .45 mil. This wire is wound at 400 turns per inch on a double mandrel (as disclosed in the Aicher patent) or 2 mil tungsten and 2.5 mil molybdenum. This primary coil is then coiled on a 6 mil'rmolybdenum mandrel at 115 turns per inch. This secondary coil is then coiled on a 20 mil molybdenum mandrel at 44 turns per inch. This results in twelve triple turns with 4.5 to 5 millimeter spacing between turns. 0bviously, there. is an appreciable resistance and no voltage drop between spaced points on the cathode coil.

The anode it is preferably made of a thin ribbon of nickel or molybdenum which, for the specific lamp referred to above. may be 4 milliso meters wide, 5 mil thick and 25 millimeters long. As shown in the drawing, the anode l2 may be made substantially U-sha'ped, the bent portion having a diameter of about 3 millimeters, so that the distance between the outer surface of the coiled cathode ii and the inner surface of the anode I2 is less than 2 millimeters and preferably about 1- millimeter. Instead of making the anode l2 U-shaped, it may be made-in the form of a cylinder. On the other hand, it may also be made in the form of a wire which may be merely anode it, the cathode ll being mounted on.

' low pressure cathode glow type capable of start- 4 'J known'bayonet pin base which is modified by spacing the pins different distances from the end of the'base, as shown in Patent No. 1,788,231, J. D. Ceader, et al., dated January 6, 1931.

vWhat I claim as new and desire to secure by Letters Patent 01 the United States is:

'.1.-A gaseous electric discharge device of the ing and operating on an approximately l2-volt velope Hi, the lamp iss'ubjected to an exhaust schedule'wherein the cathode is notactivated,

I but is outgassed at a temperature of less than 1100 C. but above the temperature at' which the carbonates will decompose. The preferred tern- ,perature'is about 1050 C. The heating is done by connecting the cathode ll acrossa suitable source of current. The correct temperature is obtained with a cathode having the proportions referred to above when the. cathode is connected with a standard GO-watt '120-volt incandescent across a source of supply, at 60 volts ih. series lamp. This heating is continued until. no more I GO: comes on. 'The lam-p is then subjected to a seasoning schedule wherein the cathodeis heat ed, bypassing current therethrough, to about 1300 C. for from t'wo'to six minutes to season the lampzand bring the arc volts and starting volts within the proper limits: which in this case are a maximum arc voltage of 9 and a. starting voltage of 12.

Alt-shown in the drawing. the lead 13 is connected to the negative terminal ll of a suitable source or current supply which may be a 1 2-volt storage battery. The lead 15 to the anode I! the positive terminal I9. The lead I is connected to the switch 20 so that, during starting. the cathode ll preheated by connecting it through the ballast I8 across the terminals I].

and IS. The close spacing of the. anode l2 and cathode ll results in ready starting of a glow discharge upon opening 01'- the switch 20. The operating discharge occurs between the anode l2 and thepoint on the cathode II at which the cathode spot appears. The-cathode spot always forms at th most negative point, providing it is as emissive as the rest of the cathode. The

. most negative point on the cathode is'the turn is connected through a ballast resistance is to adjacent to the lead wire 13, so that the dis charge is formed across the gap B. Obviously,

there isan appreciable voltage drop between the negative end of the cathode and the more positive portion opposite the anode l2. In accordance with this invention the said gap B, for the lamp specifically described herein, is greater than 2 millimeters and less than 5 millimeters,

preferably 3 to 5 millimeters.

In a lamp having the specifications described above the ballast l8 may have a resistance of about 10 ohms. I

Although I have shown and described a particular species of lamp comprising my invention, it will be obvious to those skilled in the art that various modifications may be made without departing from the spirit of the invention. In order to insure that the lead I3 is connected to the negative terminal I! of the current source upon insertion of the lamp in its socket, I prefer to use a type of base which is insertable in a socket in only one position. One such form is the wellcircuit and comprising a sealed envelope containing an ionizable gaseous medium at a pressure of the order of a few millimeters and a. stationary thermionic cathode and an anode, a pair of leadin conductors extending into said envelope and connected to the ends of said cathode for passage of pre-heating current therethrough during starting of the device, and a third lead-in con-' ductor.'connected tosaid anode, v said cathode comprisinga illamentary coil of appreciable resistance coated with electron-emissive material,

said anode being so located that it is spaced from v the negative end of said cathode a distance greater than two millimeters but less than five millimeters but being'not more than two millimeters from a portion of said cathode Which-is appreciably more positivethanit negative end.

2. A gaseous electric discharge device of the low pressure cathode glowtype capable ofstarting and'operating on an approximately l2-volt circuit and comprising a sealed envelopecontaining'an ionizable gaseous medium at a pressure of theforder of a few millimeters and a stationary thermionic cathode and an anode, a pair'of leadin conductors extending into said envelope and connected to the ends of said cathode for passage of pre-heating current therethrough during starting of the device, and a third lead-in conductor connected to said anode, said cathode comprising a filamentary coil of appreciable resistance coated with electron-emissive material, the anode being of sheet metal form of substantial area and surrounding a portion of said cathode, said anode being so located that it is spaced from the negative end of said cathode a distance greaterthan two millimeters but lessthan five millimeters but being not .more than two millimeters from a portion of said cathode which is appreciably more positive than its negative end.

3. A gaseous electric discharge device ,of the low pressure cathode glow type capable oi starting and operating on an approximately l2-volt circuit and comprising a sealed envelope containing an ionizablega'seous medium at a pressure of the order of a few millimeters and a stationary thermionic cathode and an anode, a pair of leadin conductors extending into said envelope and connected to the ends of said cathode for passage of pre-heating current therethrough during starting of the device, and a third lead-in conductor connected to said anode, said cathode comprising a filamentary coil of appreciable resistance coated withelectron-emissive material, the anode being of sheet metal having a surface area of at least sixteen square millimeters and surrounding a portion of said cathode, said anode being so located that it is spaced from the negative end of said cathode a distance greater than two millimeters but less than five millimeters but being not more than two millimeters from a portion of said cathode which is appreciably more positive than its negative end.

EUGENE LEMMERS. 

